4 ms·
Indeed you won't ever be able to ever see something fall into it, but when you get down to it that's just because the light will take an infinitely long time to
by contravariant 11y ago
Indeed you won't ever be able to ever see something fall into it, but when you get down to it that's just because the light will take an infinitely long time to reach you. There are coordinate systems that are able to describe stuff falling past the event horizon in finite time, you just won't be able to see this happening until you fall into it yourself.
- monocasa 11y agoMy question isn't along the lines of how visible it is to an outside observer, it's more of how can a singularity itself form? It seems like you can't reach infinite density in finite time given gravitational time dilation.
- contravariant 11y agoIt only takes "infinite" time in that particular coordinate system, it takes finite time in other coordinate systems, such as one where you're in orbit around the black hole.
- deleted 11y ago[deleted]
- return0 11y agoIt takes a finite amount of proper time (time experienced by the particle) to reach the singularity.
- digsmahler 11y agoAre there such coordinate systems that "describe stuff falling bast the event horizon in finite time"? How does that not violate general relativity?
- contravariant 11y agoAccording to general relativity those coordinate systems are equivalent. Well apart from the fact that the "classical" coordinate system isn't able to describe the inside of the black hole. For an example see the Kruskal coordinate system [1]. [1] https://en.wikipedia.org/wiki/Kruskal%E2%80%93Szekeres_coordinates https://en.wikipedia.org/wiki/Kruskal%E2%80%93Szekeres_coord...
- btilly 11y agoTo the first, yes. For example http://en.wikipedia.org/wiki/Lema%C3%AEtre_coordinates http://en.wikipedia.org/wiki/Lema%C3%AEtre_coordinates is one. To the second, when we talk about "coordinates" in GR, we're talking about parametrizing a volume of space-time. Given one parametrization, it is possible to create another parametrization that blows up at any particular spot - not because space-time is weird there - but because you picked a bad coordinate system. The existence of parametrizations that carry through the event horizon demonstrate that the singularity at the event horizon in Schwarzschild's original metric is not a real problem for GR. However the singularity at the middle of the black hole is a spot where GR breaks down. It is widely believed that a theory that combines GR and QM will make that singularity impossible.
- digsmahler 11y agoThank you! This will require some study.